1. Field of the Invention
The present invention relates to a pixel interpolating apparatus and a pixel interpolating method, and more particularly to a pixel interpolating apparatus and a pixel interpolating method for converging image information by an interlaced scanning in television into image information for a progressive scanning, or for a resolution conversion of image information processed by a computer.
2. Related Background Art
In the television broadcasting system, a change from a conventional analog system to a digital system is being recently investigated, and, triggered by a new technical innovation by digitization, the television broadcasting is going to further advance as information communication media and to achieve a drastic development. Digitization is already realized in a broadcasting utilizing a communication satellite (CS) or a broadcasting satellite (BS). Also digitization is investigated also for the ground wave broadcasting, and all the broadcasting waves will shift to the digital system in a near future.
An advantage of the digital television broadcasting is that plural channels are made possible, as the digital system can transmit programs of three channels within a frequency band corresponding to one channel in the analog system. This advantage can realize a new service such as a multi program (mixed multiplex program) in which a news, a sports program, a drama etc. are combined, or a multi-channel broadcasting for broadcasting three different program within a single channel.
Also the digital television broadcasting is not limited to a broadcasting of an image and an audio signal, but enables an integral broadcasting service in which various data broadcastings are added. The service including data broadcasting is classified into a multimedia-like service in which data information is added to a television program, and a service provided independently from a television program, and principal ones of such service include an observer-involving television program, a home shopping, various information services, and a weather forecast and a news that can be viewed at any time.
For matching with such digital television broadcasting, also the television receiving apparatus is showing progresses, including a thin large-sized plasma display and a cathode ray tube of a high resolution matching the digital television broadcasting. Such display apparatuses executes an image display not by a conventional interlaced scanning but by a progressive scanning. Therefore, a conventional analog television broadcasting is displayed by converting image information for interlaced scanning into image information for progressive scanning (hereinafter called IP (interlace-progressive) conversion) and also converting the image information to a resolution of the display apparatus.
(Configuration of Prior IP Conversion Process Circuit)
Now, there will be briefly explained a prior IP conversion process circuit.
FIG. 27 is a block diagram showing the structure of an ordinary IP conversion process circuit.
Field information memories 101, 102 store input image information in the unit of a field. A movement information generator 103 discriminates moving image information or still image information for each pixel by observing a difference between current input field information and field information which is inputted earlier than the current input field information by a frame period and which is outputted from a field information memory (2) 102, and judges and outputs a movement in an interpolating pixel from thus determined movement information for each pixel. A line information memory 104 stores the input image information in the unit of a line. An adder 107 executes an addition of input signals of two systems. A divider 108 determines a value of a half of the added value obtained by the adder 107. An interpolation information selector 109 selects as an interpolation pixel value, according to an output signal from the movement information generator 103, either pixel information inputted earlier by a field period than the current input field information or an average value of the pixel values of upper and lower lines of an interpolation pixel position, outputted from the divider 108. Input/output speed converters 105, 106 respectively store the pixel information outputted from the interpolation information selector 109 and the input pixel information, in the unit of a line, and execute readouts of the stored pixel information at a twice speed of the input image information. A display information selector 110 outputs the pixel information from the input/output speed converter (1) 105 and that from the input/output speed converter (2) 106 alternately for every line.
(Function of Prior IP Conversion Process Circuit)
In the following, there will be explained functions of the prior IP conversion process circuit described above.
Input image information for interlaced scanning is supplied to the field information memory (1) 101 and the line information memory 104, from which pixel information delayed by a field period and pixel information of a preceding line can be respectively obtained. FIG. 28 shows a mode of image information display in an NTSC (national television system committee) displayed by an interlaced scanning. In the NTSC signal, an image is constituted of 525 horizontal lines and is called a frame. Such frame is divided, by an interlaced scanning, into an odd field representing odd-numbered lines as shown in (b) and an even field representing even-numbered lines as shown in (c), and the NTSC signal displays image information of 525 lines by alternately displaying an image of the odd field and an image of the even field. Thus the odd field and the even field mutually interpolate the information of deficient lines. Therefore, referring to FIG. 27 again, pixel information of a preceding field corresponding to the position of the pixel to be interpolated is obtained from the field information memory (1) 101, and pixel information in upper and lower lines of the pixel to be interpolated is obtained from the input image information and the line information memory 104. Also averages of pixel information in the upper and lower lines of the pixel to be interpolated are obtained by the adder 107 and the divider 108 from the input image information and the line information memory 104, and are used as interpolation pixel information in a moving image.
The pixel information outputted from the field information memory (1) 101 is further delayed by a field period by the field information memory (2) 102, thereby providing image information delayed by a frame period from the input image information, namely pixel information of a preceding frame corresponding to the input pixel position.
In the following there will be given an explanation on the movement information generator 103.
FIG. 29 is a block diagram of an embodiment of the movement information generator 103.
Referring to FIG. 29, a subtractor 1031 determines a difference between the currently inputted field information and field inputted earlier by a frame period than the currently inputted field information and outputted from the field information memory (2) 102. An absolute value device 1032 determines an absolute value of the difference obtained by the subtractor 1031. A threshold filter circuit 1033 compares the value determined by the absolute value device 1032 and a predetermined threshold value, and, in case the value determined by the absolute value device 1032 is smaller than the threshold value, judges the pixel as a still image and outputs a value “0”, but, in case the value determined by the absolute value device 1032 is equal to or larger than the threshold value, judges the pixel as a moving image and outputs a value “1”, whereby, even in case the input image information includes inappropriate pixel information such as a noise, the influence of a certain fluctuation can be eliminated. A line movement memory 1034 stores, in the unit of a line, movement information of each pixel outputted from the threshold filter circuit 1033, whereby movement information earlier by a line than the input image information can be obtained. An interpolation pixel movement information generator 1035 judges and outputs, from the movement information outputted from the threshold filter circuit 1033 and the movement information of a preceding line outputted from the line movement information memory 1034, movement information of an interpolation pixel generated between these lines.
Again referring to FIG. 27, the interpolation information selector 109 selects and outputs, as interpolation pixel information, pixel information outputted from the field information memory (1) 101 or the pixel information outputted from the divider 108 respectively in case the movement information outputted from the movement information generator 103 is “0” or “1”.
The input/output speed converters (1) 105 and (2) 106 respectively store, in the unit of a line, the interpolation pixel information outputted from the interpolation information selector 109 and the input image information, then the stored pixel information is read out with a speed twice of the speed of the input image information, and the pixel information outputted from the input/output speed converter (1) 105 and the pixel information outputted from the input/output speed converter (2) 106 are outputted alternately for every line by the display information selector 110.
In the prior IP conversion method explained above, the pixel information of the generated interpolation pixel becomes different depending upon whether the input image information is a moving image or a still image. More specifically, in case of a still image, the pixel information inputted earlier by a field period, outputted from the field information memory (1) 101, is used as the pixel information for the interpolation pixel, thereby generating the pixel information faithful to the original image information. On the other hand, in case of a moving image, an average value of the pixels positioned in the upper and lower lines of the pixel to be interpolated, outputted from the divider 108, is used as the pixel information for the interpolation pixel, thereby resulting in various deteriorations in the image quality, in comparison with the original image information. Particularly the defects appear in case the original image information includes a slope in an oblique direction as shown in FIG. 30. FIG. 31 shows a state where the original image information shown in FIG. 30 is inputted by an interlaced scanning of every other lines and is subjected to an interpolation process for a moving image by the IP conversion process circuit shown in FIG. 27. As will be apparent from FIG. 31, in case of the interpolation process as a moving image by the IP conversion process circuit, the image information which originally has a smooth slope in the oblique direction as shown in FIG. 30 is interpolated as image information with stepwise changes, thus providing an image lacking smoothness.
FIG. 32 indicates, as another example having a slope in the oblique direction, image information of an oblique line with a line width corresponding to a pixel. FIG. 33 shows a result in case such image information is inputted by an interlaced scanning of every other lines and is subjected to an interpolation process as a moving image similarly by the IP conversion process circuit. Such image information including an oblique line with continuous pixel values is thus displayed as a broken line.
Against such problem, proposals are made, for example in Japanese Patent Application Laid-open No. H06-153169, Japanese Patent Application Laid-open No. 2000-115720, Japanese Patent Application Laid-open No. 2001-218169, Japanese Patent Application Laid-open No. 2001-218170, Japanese Patent Application Laid-open No. 2002-252834, Japanese Patent No. 2990737 and Japanese Patent No. 2996099 of referring to a combination of two pixels plural inclined directions with respect to a center pixel to be interpolated and determining the pixel information of the interpolation pixel from a combination with a small difference.